Signaling system



y 1937. o. MITCHELL ET AL 2,087,352

SIGNALING SYSTEM Filed June 9, 1956 l Lww L Comb-06 Device mvEh oRs Y ztclzelli BY L. 6'. Ira/20mm ATTQRNEY Patented July 2@, 1937 UNE'E'E .ETATES PATENT QFH'CE SIGNALING SYSTEM Application June 9, 1936, Serial No. 8 1,374

(Cl. ills-A l) an alternating current of constant amplitude, then the vogad will be set in accordance with that amplitude and the power delivered will be considerably higher than would be the case of a speech message having peaks substantially of 5 the same value as the amplitude of the steady alternating current. This may lead to overloading of repeaters and other undesirable characteristics, and the purpose of this invention is to provide means whereby the gain of the vogad is 10 definitely lower if a constant alternating current is impressed at the input than would be the case if it were set in the same way as it would be for speech; that is, the purpose is to over- 9 Claims.

This invention relates to a signaling system, and more particularly to a telephone communication system containing a voice operated gain adjusting device, commonly called a vogad, which possesses the characteristic of delivering to the transmission line speech waves of substantially constant volume independently of whether the speaker is a weak or a strong speaker. This application is a continuation as to common subject matter of our application Serial No. 45,644, filed October 18, 1935.

In such a transmission line it is common to transmit a ringing current of a definite frequency and constant amplitude, or to make tests from time to time on the transmission characteristics come the tendency of the vogad to adjust itself 15 of the line, and to do this latter with alternating for too high a gain for a steady alternating curcurrents of definite frequency and constant amrent.

plitude, the frequencies chosen for testing lying Another purpose of the invention is to provide preferably in the signaling range. The type of means which will operate an alarm or give some circuit here in mind is that known as a fourother suitable signal if the output of testing cur- 20 Wire circuit, and the vogad used with it is placed rent from the vogad to the line does not lie within the transmitting side at the terminals. The in certain limits, thus indicating that some porvogad is of the type shown in patent to Hogg tion of the circuit, and in particular the vogad,

et al., No. 1,853,974, April 12, 1932, and consists is not functioning properly.

essentially of a variable gain device or vario-re- The invention will be better understood by peater, the gain being determined at any time reference to the following specification and the by the volume of the signal coming to the input omp y w in which Figure 1 S OWS of the gain device. This variable gain device or a transmission line with avogad and the elements repeater has associated with its input a gain inwhich comprise the means to carry out our invencreaser which functions to increase the gain of tion; Fig. 2 shows the invention applied to volume the repeater when the incoming speech is above control devices other than the vogad; and Fig. 3

a certain predetermined minimum power level, shows a portion of such means in greater detail.

and does this ordinarily by changing the charge Referring more specifically to Fig. 1, there is on a condenser placed in the grid circuit of the shown a four-wire circuit consisting of the lines repeater. There is also associated with the re- L1 and L2 with terminating sets i and 5 by which peater at the output side a gain increase disthe transmission line is transformed from a twoabler' which serves the function when the output wire to a four-wire basis, or the reverse. For

of the repeater exceeds a certain predetermined simplicity a single line is shown for circuit L1 amount of opening a circuit in the gain increaser and also for L2 but it is to be understood that in such manner as to isolate the biasing condenser these are actually each a pair of wires. On the 40 in the grid of the vario-repeater. Also connected transmitting side of the circuit at the terminal to the output of the repeater is a gain decreaser i, there is introduced a vogad l with supplewhich serves the function when the output exmentary apparatus to be described hereinafter.

coeds another higher predetermined value of The vogad comprises the vario-repeater 8, the

changing the charge on the biasing condenser in gain increaser 9, the gain increase disabler i9 such a direction as to decrease the gain of the and the gain decreaser H, the details of the oprepeater. eration of which are all described in such a The vogad as a whole has the characteristic patent as that to Hogg et al., referred to above.

of responding rather slowly to the typical peaks Identical equipment ii is shown on the transmitof a speech message, bearing in mind that the ting side at the terminal 5. The circuit also actual power of the speech message delivered by shows on the receiving side, at each terminal, a

the repeater is well below what it would have been reverse vogad 2i and 2'2 also terminal echo supwere the amplitude of the output constant and pressors 23 and 2d and gain change suppressors of a value corresponding to the peaks. If, now, 25 and 26, the arrangement and the performance there is impressed on the input of the vogad of which are fully described in such a circuit as shown in application of Wright and Abraham, Serial No. 752,150, filed November 8, 1934, now Patent No. 2,943,403, issued June 9, 1936, and the circuit as thus far described does not constitute a portion of this invention.

As stated above, it is sometimes desirable to send i -ging current over such a circuit or to send testing current, in both cases the currents being alternating and of constant amplitude. Also, as pointed out, the gain of the vogad in this case is set at too high a value. Such a source of alternating current is shown at E2 the terminal and it is to be understood that it may be associated with the transmission line in any suitable manner, indicated conventionally only in the drawing.

In Fig. 1 two methods are shown for overcoming the d "ficulty. Que of these shown in connection with the vogad l and the other is shown in connection with the vogad ll. A description will be first given for that shown in the vogad ii. In the circuit derived from the output of the repeater 8 and which normally supplies power to the elements ill and ii, we place a loss device 3i which may consist of a resistance network, represented here by a single resistance element. Beyond this element 3! and at the input of the elements l9 and H there is a derived circuit which then goes through a circuit T tuned to the frequency of the ringing current or the Having passed testing current. through the tuned circuit T, the alternating current passes through an amplifier-detector to control a slow-operate relay M which, in case is operated, will short-circuit the element 35, hus effectively rendering the gain increase disabler and the gain decreaser more sensitive so that the repea er 8 is not adjusted to so high a gain for a given output as when the element 35 is in the circuit. The sensitivity of the relay is adjusted so that it will operate and short-circuit the element 95 on ringing or testing current.

She device thus far described carries out one or" the purposes of our invention, namely, to reduce the gain of the vogad for steady alternating current input. In addition, however, it may be desired that an alarm shall be given in the event that this portion, or some other portion, of the vogad assembly is not functioning in a manner to give an output which is between cerdesired limits. To this end we supply the equipment shown at 49 which comprises an alarm A to be operated from a battery ll. This alarm cannot in any case be operated unless the circuit from the battery ll is closed at the point it by of a circuit 33 derived at the output of the slow-operate relay at, and this derived circ it in turn does not function unless steady alternating current of a frequency which will pass the timed circuit '1" is present. In case the circuit is closed, then the alarm may be operated through one of two paths. The first of these traces through the circuit which circuit is normally closed at the point 56 if the power on the transmission line is less than a lower specified. limit, under these conditions the alarm will be sounded to call attention to the abnormal condition. If the power on the line exceeds the specified value, then the circuit at is broken by the amplifier-detector L and no alarm is sounded. In case the power on the lin exceeds a certain higher specified value, then the circuit at 6B is closed through operation or the amplifier-detector H and again the alarm A gives an indication calling attention to an abnormal condition. The power value on the line at which the amplifier-detector H will function can be adjusted as desired by such a means as the loss element 49. As a result of these circuit arrangements it is evident that We have accomplished the. second purpose of our invention, namely, to provide a signal device which will give a suitable alarm in the event that the power on the transmission line is at too low or too high a value.

The second method by which we accomplish the purposes of our invention is shown at H at the right-hand side of Fig. 1. In this arrangement the same type of vogad comprising a variorepeater, a gain increaser, a gain decreaser, and a gain increase disabler is shown with the elements in the same relationship to each other as in the equipment at l but without the loss element 35 of i. In series with the transmission line is a loss element 51, normally short-circuited at In case, however, a ringing current or a testing current is impressed on the line, a portion of this current will pass through a derived circuit including the tuned circuit T, the amplifier-detector 53 and the slow operate relay which may b identical to the corresponding tuned circuit and relay of l. Such steady alternating current causes operation of the relay E -l, opening the short circuit at 52 and thus introducing the loss 51 in series with the line, the loss being of such value as to bring the alternating current power to the desired value. The alarm device in this case is also analogous to that previously described and is indicated by 49, the circuits of 43 being controlled by the derived circuit 56 from the output of the relay 54.

The description up to this point has dealt with the application of a special tone operated cir cult to a vogad. It is, however, quite possible to apply this same means of tone adjustment to any volume control device. Such volume control devices might be in the form of compressors or expanders as described in a patent to Green, No. 1,738,090, dated December 3, 1929, or a device such as the half-vogad which is described in a patent to Doba, No. 1,854,828, dated April 19, 1932.

Referring to Fig. 2, a transmitting volume control device i is shown in the outgoing transmitting line. At the output of this device the tuned circuit 32, amplifier-detector 33, and slow-operate circuit 34 are shown. When the slow-operate circuit operates it inserts the loss 3| in. the line. At the same time it operates the alarm device 46, which is identical with the alarm device shown in Fig. 1. Thus, if the volume control device I is operating correctly, the proper value of testing tone is sent out on the line, but if it is operating incorrectly, the alarm device 4% will indicate this immediately.

t the receiving end of the circuit another volume control device I is used. This device may be completely independent of the transmitting volume control device at that end of the circuit. At the output of this device the same mecha nism is indicated, a tuned circuit 32, amplifierdetector slow-operate circm't 34, and an alarm circuit ll). However, in this case it is assumed that it is desirable to increase the amount of testing power over that which is normally put out by the volume control device I. Thus, operation of the slow-operate circuit removes the loss 3|, thereby increasing the testing power supplied to the two-wire line.

It will be obvious from the above that the general principle of an auxiliary tone adjusting device for volume control circuits might be applied to a large variety of volume control devices.

The tuned circuit and slow-operate relay in any of the modifications shown may take on a variety of forms. One form which is suitable for carrying out our invention is shown, for illustrative purposes only, in Fig. 3 and comprises a high impedance input to an amplifier-detector. This high impedance input may be obtained in a wellknown manner by means of condensers C1, C2 and C3, along with the inductance of the transformer, all adjusted to respond only to the ringing current or testing frequency which it is desired to use. From the input coil the waves affect the amplifier-detector and, if strong enough, cause a current to flow in the plate circuit of this detector. Alternating current components are bypassed by the condenser C4 and the direct current operates the master relay iii? which, in turn, initiates the release of the test zone relay 61!. This latter, which is. normally held operated, remains operated for a considerable length of time due to the charging up of the condenser C5 through the high resistance 63 and the windings oi the relay 6!, thus making effectively a slow-operate circuit.

The release of the relay 6! is made to perform the desired function in the vogad circuit.

It is obvious that many changes may be made in the circuit arrangement. For example, instead of having the circuit T tuned to a single frequency it could be designed to permit passage of any desired number of chosen frequencies, and this in general might be desirable because a proper testing of the transmission line would call for measurements at several of the frequencies in the signaling range and these might all be different from the ringing frequency. Furthermore, it might be desirable in some cases to use two or more control units, one for testing current and one for ringing current. There might also be certain circuit arrangements where a vogad would be used at only one end of the circuit.

What is claimed is:

1. In a volume controlled circuit, a vogad adapted to deliver substantially constant value of speech message to the line, the gain of the vogad being set by the peak values or" the incoming speech to it, a source of alternating current of constant peak voltage for occasional impression on the line, and means when said alternating current is present to reduce the gain of the vogad with reference to the normal gain for that input peak voltage.

2. In a volume controlled circuit, a vogad adapted to deliver substantially constant volume of speech message to the line, the gain of the vogad being set by the peak values of the incoming speech, a source of alternating current of constant peak voltage for occasional impression on the line, and means when said alternating current is present to introduce loss in the main transmission line to reduce the eiiective transmission level of the line over that normal for speech message of the same peak voltage as the alternating current source.

3. The combination of claim 1 characterized by the fact that the means for reducing the gain of the vogad with reference to the normal gain go to the line, the gain of the the peak values of the incomof alternating current of voltage for occasional impression e line and when said alternating cureduce the gain of the vogad ing speech, a

..it peak peak vol age and to operate an alarm if the vogad 1' said alternating current is of abnorcontrolled circuit, a vogad r substantially constant volume of speech. message to the line, the gain of the vogad homg set by the peak values of the incomspeech, a source of alternating current of constan voltage for occasional impression on the l e and means when said alternating current is present to reduce the gain of the vogad with ref rence to the normal gain for that input ealr. volt and to operate an alarm if the vogacl outpt said alternating current is below a spec- .ed value and above another specified value.

7. The combination of claim 1 characterized by the fact at the 11 .112; for reducing the gain oi the vogad with reference to the normal gain ts of a resistance network in the derived it at the output of the vogad leading to the vogad con is, the being short-circuited when the constant alternating current source is connected i.-.

8. in a vein controlled circuit, a vogad i e to the line, the gain of the oy the peak values of the incomsource of alternating current of voltage for occasional impression of the line over of the same rent so rce normal for speech message voltage as the alternating curto operate an alarm if the vogad constant alternating current is d value and above another speci- DUI EN MITCHELL. LEONARD G. ABRAHAM. 

